Timing and duration of hatching in gynogenetic, triploid, tetraploid, and hybrid progenies in rainbow trout

Abstract

Mean duration of embryonic development and variability of this parameter were studied for seven different progenies in rainbow trout : diploid controls, diploid gynogenetics, triploids resulting from heat shock or from a direct cross between diploid female and tetraploid male, tetraploids, and diploid or triploid hybrids between female rainbow trout and male coho salmon. The main results were : (1) gynogenesis does not change mean duration of embryonic develop- ment, but induces larger variability of this parameter ; (2) the higher the ploidy level the shorter the duration of embryonic development : tetraploids hatch before the two types of triploids, which hatch before the diploid controls. On the other hand, within group variability of hatching time is generally greater in these groups than in the control ; (3) in the case of interspecific hybridization, triploidy also reduces duration of embryonic development, relatively to diploid hybrids, but induces greater homogeneity in hatching times than in diploid hybrids.